Accumulator with plastic casing

ABSTRACT

So that an accumulator having a gas-tight and liquid-tight, electrolyte-filled casing in which are arranged electrodes which are separated from each other by a separator and which are each electrically connected to pole contacts accessible from the outside of the casing can be produced in an advantageous manner from the point of view of the manufacturing procedure, wherein the accumulator is to have a durably and reliably sealed casing which is not restricted in terms of its shape, it is provided that in the region of the pole contacts the casing comprises a soft plastic material and a hard plastic material which are fixedly connected together, the soft plastic material forming a seal for the pole contacts and/or the feed-through ducting means of the pole contacts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns an accumulator with a gas-tight and liquid-tightelectrolyte filled casing in which electrodes are separated from eachother by a separator and are respectively electrically connected to polecontacts that are accessible from outside of the casing.

2. Discussion of the Prior Art

Accumulators of that kind are known with a large number of differentcasing shapes. A conventional alkaline accumulator has a cylindricalcasing which comprises metal and forms a pot-shaped, electrolyte-filledcontainer both for the electrodes and also for the separator. The coverwhich holds the positive pole contact is fitted into the opening of thepot configuration. In that case the flanged-over edge forms a holdingarrangement which is both gas-tight and also liquid-tight. However, ametal casing of that kind is difficult to produce when dealing withnon-round and in particular rectangular cells.

The use of plastic casings is known for lead-acid accumulators and makesit possible to produce rectangular casings, while making good use of theavailable space. This construction however cannot be applied to alltypes of accumulators. The metal pole contacts which are cast into theplastic material casing or the metal feed-through ducting means thereofare of different coefficients of thermal expansion from the plasticmaterial, but nonetheless may not became leaky upon an increase intemperature during charging or discharging at high current levels. It isnecessary throughout the entire service life of the accumulator toensure that neither gas nor electrolyte accidentally escapes.Accumulators with a very low internal resistance such as for examplealkaline nickel-cadmium or nickel-metal hydride accumulators may buildup greatly increased internal pressures under a high current loading,and such pressures should not result in leaks occurring in the region ofthe pole contacts.

Seals which are fitted between the casing and the pole contact, such asfor example the elastic round-cord rings which are referred to asO-rings require an additional production step in terms of inserting andcorrectly positioning the seal and therefore have an adverse effect onthe production costs of the accumulator. Difficult electrolytes which,by virtue of a high capillary action, have a tendency to creep underseals, such as for example caustic potash solution, which additionallyexhibits a migration movement in the direction of negative potential,can escape from the casing if the seal is not correctly inserted or ifthe seal is subsequently mechanically displaced, and they cansubsequently give rise to damage.

EP-A1-0 089 619 describes a gas-tight and liquid-tight pole sealingarrangement which is desired in particular for lead accumulators whosecasing consists of plastic material. For sealing purposes, there isproposed therein a sealing system which comprises a plurality of layersof different materials and in which inter alia a free chamber isdesigned to surround the pole contact, and melt adhesives and furtherseals are arranged on that chamber. However that pole sealingarrangement can only be produced by a considerable number of productionsteps.

U.S. Pat. No. 5 197 994 discloses thermal casing welding procedures inrespect of battery casings which comprise plastic material.

EP-A2-0 538 039 discloses an inserted cap which comprises a sealingmeans and which, in the case of a cylindrical battery, holds the centralelectrode and the pole contact relative to the casing and at the sametime forms a seal for the battery casing to prevent fluid from escaping.

SUMMARY OF THE INVENTION

Consequently the object of the present invention is to provide anaccumulator which is advantageous in terms of production from themanufacturing process point of view and which has a durably and reliablysealed casing which is not restricted in terms of its shape.

That object is attained by an accumulator with a gas-tight andliquid-tight electrolyte filled casing in which electrodes are separatedfrom each other by a separator and respectively electrically connectedto pole contacts that are accessible from outside the casing, wherein ina region of the pole contacts the casing comprises a soft plasticmaterial and a hard plastic material fixedly connected together and thesoft plastic material forms a seal for the pole contacts and/or for afeed-through ducting means of the pole contacts.

Making the casing in the region of the pole contacts from a soft and ahard plastic material which are fixedly connected together makes itpossible to use the soft plastic material as a seal for the polecontacts and/or for the feed-through ducting means of the pole contacts.In that respect displacement of the seal due to external influences canbe prevented by the mechanical connection between the two plasticmaterials. This design configuration also provides that there isessentially only one sealing surface, namely the sealing surface betweenthe soft plastic material and the pole contact and/or the feed-throughducting means thereof. Therefore the electrolyte or the gas developedthereby can no longer escape along a second sealing surface between theseal and the casing. Furthermore, a sealing contact of the soft plasticmaterial against the pole contact or the feedthrough ducting meansthereof can be so designed that the sealing surface is greatly enlargedand fluid has to creep under long distances if it is to be escape.

This design configuration is advantageous from the point of view ofmanufacturing procedure as, after the soft and the hard plasticmaterials are joined together, suitable openings for the pole contactscan be formed therein, for example by stamping, with a high degree ofaccuracy. Alternatively, a pole contact or its feed-through ductingmeans, which is already held in the hard plastic material, can besubsequently surrounded by the soft plastic material in a hot-in-hotinjection welding process. That gives in each case a connection betweenthe soft and the hard plastic materials, over the full surface areathereof.

As both plastic materials essentially comprise the same thermoplasticelastomer and differ from each other in terms of their hardness eitherby a differing addition of plasticisers or by virtue of a differentdegree of cross-linking, there are no detrimental thermal stressesinvolved. The choice of the thermoplastic elastomer makes it possible touse chemically inert materials, such as for example modified polyamides,styrene-ethylene-butylene-styrene copolymers or polypropylenes whichhave excellent levels of resistance relative to the electrolyte.

Highly developed production procedures which are available at thepresent time for shaped plastic members such as for example injectionwelding can be used without limitation, whereby the shape of the casingis no longer restricted.

In a preferred embodiment the pole cap of the pole contact is connectedto the feed-through ducting means thereof by spot welding and engagescup-like over a part of the soft plastic material. That increases thecreep distance under the seal, by the area with which the soft plasticmaterial bears against the pole cap. The pole cap is correctlypositioned upon being subsequently fitted to the feed-through ductingmeans, by the soft plastic material.

An alternative embodiment uses a pole contact which comprises asubstantially cup-shaped rivet and the rearward end of which, in themanufacturing operation, is flanged over in such a way that it engagesbehind a part of the hard plastic material. In that situation, the frontregion of the pole contact is always securely held in sealing contactagainst the soft plastic material by the flanged-over part of the rivet.In that respect, in a manner which is advantageous from the point ofview of the manufacturing procedure involved, the flanged-over part ofthe rivet may engage behind a conductive tongue which is insertedbetween the rivet and the casing and which makes the electrical contactwith the respective electrode. In that way both the pole contact can befitted in position and also the electrical connection thereof can bemade in a single working step by riveting, in an inexpensive operatingprocedure.

A further improvement in regard to manufacturing procedure is achievedif the casing of the accumulator includes between two casing portions avolume which extends therearound and which, in the operation ofinjection welding of the soft plastic material, can also besimultaneously filled. The soft plastic material within that volumeadvantageously serves as an additional casing seal but does not requireany manufacturing step of its own.

If both casing portions comprise a plastic material of approximately thesame hardness, they can be securely and durably sealingly connectedtogether by ultrasonic welding in an overlapping region.

In an alternative configuration both casing portions are held togetherby retaining elements which are disposed in an overlapping region. Inthat way the casing portions can be securely joined together by beingsimply pressed together in an operation which is advantageous from thepoint of view of the manufacture procedure involved. If, after the twocasing portions have been latched together, the soft plastic material isintroduced into the volume extending around the casing, the soft plasticmaterial and the hard plastic material of the two casing portions aresealingly joined together over their full areas by virtue of the weldingoperation in that region. If the two casing portions are latchedtogether after the operation of injecting or spray welding the softplastic material, the retaining elements guarantee that the hard plasticmaterial of the one casing portion bears sealingly against the softplastic material of the other casing portion.

By embedding glass fibres in the plastic material, preferably in aproportion by volume of about 40%, it is possible markedly to improvethe mechanical properties of the casing, such as its impact strength,its breaking load-carrying capacity and its flexural load-carryingcapacity.

With a rectangular accumulator casing in which the electrodes arearranged in superposed relationship in a layer-wise manner respectivelyseparated by the separator, it is possible to eliminate unused volumesand it is possible to provide an accumulator of high capacity.

In the case of gas-tight alkaline accumulators such as for examplenickel-cadmium or nickel-metal hydride accumulators, a desired-rupturelocation can be disposed as a portion of reduced thickness, within thecasing portion which comprises hard plastic material. That prevents theaccumulator from exploding in the event of an abrupt rise in internalpressure by virtue of specific gas discharge by way of thedesired-rupture location.

Subsequent filling of the accumulator with the electrolyte is madepossible by virtue of a closable filling opening. Arranging the fillingopening closer to the positive pole contact than to the negative polecontact reduces the creep effect when using caustic potash solution asthe electrolyte.

In another embodiment the casing of the accumulator at the same timealso forms a part of a casing of an electrical device. That makes itpossible for example to simplify the construction of portableradiotelephones and to reduce the size of the accumulator, in spite ofthe accumulator being of high capacity.

DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter with referenceto the drawings in which:

FIG. 1 is a partly cross-sectional view through an accumulator of afirst embodiment according to the invention with a cup-shaped pole cap,

FIG. 2 is a partly cross-sectional view through an accumulator of asecond embodiment according to the invention with a rivet-like polecontact,

FIG. 3 is a view in cross-section through an accumulator according tothe invention with a rectangular casing and pole contacts arranged onone side of the casing,

FIG. 4 is a view in cross-section through the accumulator in FIG. 3along line A--A,

FIG. 5 shows an accumulator structural group mounted on a casingportion, during an intermediate step in production,

FIG. 6 is a view in cross-section through an accumulator with arectangular casing and pole contacts arranged on two opposite sides ofthe casing, and

FIG. 7 is a view in cross-section through the accumulator of FIG. 6along line B--B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the Figures, the same or similar components of different embodimentsare each denoted by the same references.

Without limitation in respect of the large number of designconfigurations which are possible by virtue of the present invention, arectangular gas-tight and liquid-tight alkaline accumulator is describedhereinafter. In that respect, the term gas-tight and liquid-tight isused in relation to accumulators to denote accumulators which do notallow either gases or liquids to escape under normal operatingconditions but which can intentionally form openings when predeterminedconditions are attained, such as for example a predetermined increasedpressure.

The accumulator 1 has a casing which comprises two portions 2 and 3 andwhich surrounds the positive electrode 5 and the negative electrode 6.The electrodes 5 and 6 are separated from each other by the separator 4.In the condition in which it is ready for operation the accumulator 1 isfilled in known manner with an electrolyte which is not shown in theFigures.

In the region of the pole contacts 7, 8 the casing is in two layers,comprising a layer of a hard plastic material 24 and a layer of a softplastic material 14. The soft plastic material 14 which is shown bycrossed hatching in the Figures is welded over the entire surface areato the hard plastic material 24 which is shown by inclined-linehatching.

With the hot-in-hot injection welding process which is used the weldedsurface is formed upon injection of the soft plastic material 14 alongits contact surface relative to the hard plastic material 24. By virtueof the addition of plasticisers or by the choice of its degree ofcross-linking, the soft plastic material 14 is of an adjustable hardnesswhich is in the range of known sealing materials. The hardness of thehard plastic material is so adjusted that it reaches the usual levels ofcasing strength.

The materials used are modified polyamidesstyrene-ethylene-butylene-styrene-copolymers and/or polypropylene. Theportions of the casing 2, 3, which comprise plastic material, each havea peripherally extending overlapping region 9, 10 in which they are incontact with each other over a surface area. The portions 9, 10 are heldtogether by an ultrasound welded seam 11 extending therearound.

In a further configuration according to the invention, formed above theoverlapping region 9 and enclosed by the region 10 is a volume 12 whichextends around the periphery of the arrangement and which is connectedby way of a passage 13 to the volume of the soft plastic material 14 inthe region of the pole contacts 7, 8. That volume 12 is alsosimultaneously filled in the operation of injection welding of the softplastic material 14. The soft plastic material 14 within the volume 12is thus formed integrally with the soft plastic material 14 in theregion of the pole contacts 7, 8 and is also welded over its full areato the hard plastic material 24.

In an alternative configuration the mechanical connection between thetwo casing portions 2, 3 is provided by retaining elements 30, 31arranged in the overlapping region 9, 10. In that case, in the latchedcondition, a peripherally extending retaining projection 31 on the onecasing portion 3 engages behind a peripherally extending groove 2 in therespective other casing portion 2. Assembly of the two portions 2, 3 ismade easier by virtue of the retaining projection 31 having an inclinedrun-on surface 32. Within the volume 12 the soft plastic material 14 iseither connected over the full surface area by injection welding to bothregions 9, 10 or it is only connected by injection welding to the region10 and the retaining elements 30, 31 hold the region 9 in contactagainst the soft plastic material 14, with a sealing effect at the end.

Glass fibres or other known inert fibres are optionally embedded intothe hard plastic material 24. In that case a proportion by volume ofglass fibres of about 40% is preferred.

A desired-rupture location 15 in the form of a portion of reducedthickness is arranged within the casing portion 2, 3 which compriseshard plastic material 24. The desired-rupture location 15 is of adefined area and thickness, which are so adjusted that, as from a givenincreased pressure within the accumulator casing, an opening is formed,which results in the pressure being reduced.

In the case of accumulators which are filled with caustic potashsolution as the electrolyte, a through opening 16 is preferably arrangedin the vicinity of the positive pole contact 7 and is of a substantiallyT-shaped profile. That opening 16 is closed by a T-shaped plug 17 afterthe filling operation.

A first embodiment includes pole contacts 7, 8 with a frustoconicalfeed-through ducting means 18, over which engages a cup-shaped pole cap21. The frustoconical feed-through ducting means 18 bears with itslaterally enlarged edge portion against the hard plastic material 24 insurface contact therewith and is held in a self-centred condition in athrough opening 20 which is also frustoconical. The cup-shaped pole cap19 is connected to the feed-through ducting means 18 by spot welding andengages over the soft plastic material 14 in sealing contactthereagainst. One or more spot welds 21 can be produced both prior toinjection of the soft plastic material 14 and also thereafter. In thelatter case, in known manner, the heat energy introduced in the weldingoperation is so selected that plastic deformation of the soft plasticmaterial 14 and the hard plastic material 24 which forms the throughopening 20 is prevented.

In an alternative embodiment the pole contacts 7, 8 are of asubstantially T-shaped cross-section whose radially enlarged regionrepresents the pole caps 19 and forms an integral transition into thefeed-through ducting means 18. The ducting means 18 has an internalspace 22 which is cylindrically hollowed out and which forms a cup-likerivet and which permits the end 23 to be flanged over. The flanged-overend 23 engages behind a part of the hard plastic material 24 in theregion of the pole contacts 7, 8. In that way the pole cap 19 is durablypressed in sealing contact into the soft plastic material 14.

In a further embodiment, inserted between the flanged-over end 23 andthe hard plastic material 24 is an electrically conductive tongue 25which consists of metal and which makes a respective connection to eachof the electrodes 5 and 6. The tongue 25 is connected by a spot weld 26to connecting lugs 27, 28 which laterally project from the electrodes.The electrodes 5, 6 are arranged in the casing 2, 3 of the accumulator 1in superposed relationship in a layer-like arrangement, as shown inFIGS. 2 and 3. Alternatively the electrodes 5, 6 are folded one over theother in a meander-like configuration, with the interposition of theseparator 4, as shown in FIG. 6.

In this embodiment which preferably includes a respective pole contact7, 8 at each of oppositely disposed sides of the casing, the electrodecarrier of the positive electrode 5 is directly connected to thefeed-through ducting means 18 while the feed-through ducting means 18 ofthe negative pole contact 8 is connected directly to the negativeelectrode 6 or to a strip 29 which is in contact with the negativeelectrode 6.

By virtue of the two-part casing structure, the electrodes 5, 6 caninitially be fixed during manufacture to the pole contacts 7, 8 and acasing portion 3, by means of the connecting lugs 27, 28 of theelectrodes 5, 6. Such an accumulator structural group is shown in FIG.5, wherein the pole contacts 7, 8 are already sealingly held within thesoft plastic material 14 and the hard plastic material 24.

Such a structural group can both be connected to the casing portion 2shown in the Figures, and also fitted into a corresponding casing of anitem of electrical equipment. The accumulator 1, with its casing, thenforms a part of the casing of the item of electrical equipment.

What is claimed is:
 1. An accumulator with a gas-tight and liquid-tightelectrolyte-filled casing, in which are arranged electrodes that areseparated from each other by a separator and are respectivelyelectrically connected to pole contacts that are accessible from outsideof said casing, whereinin a region of said pole contacts (7, 8) saidcasing (2, 3) comprises a soft plastic material (14) and a hard plasticmaterial (24) that are fixedly connected together, and said soft plasticmaterial (14) forms a seal for at least one of said pole contacts (7, 8)and a feed-through ducting means of said pole contacts.
 2. Theaccumulator according to claim 1, wherein said soft plastic material(14) and said hard plastic material (24) have been connected together byinjection welding over their full areas.
 3. The accumulator according toclaim 1, wherein said soft plastic material (14) and said hard plasticmaterial (24) comprise a thermoplastic elastomer.
 4. The accumulatoraccording to claim 3, wherein said thermoplastic elastomer is selectedfrom the group consisting of modified polyamide,styrene-ethylene-butylene-styrene copolymer and polypropylene.
 5. Theaccumulator according to claim 1, wherein at least one of said polecontacts (7, 8) has a pole cap (19) that has been connected to saidfeed-through ducting means (18) by spot welding and engages cup-likeover a part of said soft plastic material (14).
 6. The accumulatoraccording to claim 1, wherein said feed-through ducting means (18) formsa substantially cup-shaped rivet having a flanged-over end (23) thatengages behind part of said hard plastic (24) so that at least one ofsaid pole contacts (7, 8) and said feed-through ducting means (18) isheld in sealing contact against said soft plastic material (14).
 7. Theaccumulator according to claim 6, wherein said flanged-over end (23)engages behind a conductive tongue (25) inserted between said rivet andsaid casing.
 8. The accumulator according to claim 1, wherein saidcasing (2, 3) includes a volume (12) that extends around said casingbetween two casing portions (2, 3) and is filled with said soft plasticmaterial (14) as a seal.
 9. The accumulator according to claim 8,wherein said soft plastic material (14) within said volume (12) and saidsoft plastic material (14) in said region of said pole contacts (7, 8)are joined together.
 10. The accumulator according to claim 1, whereinsaid casing (2, 3) is comprised entirely of plastic material (14, 24)and said casing comprises two casing portions (2, 3) that have beenjoined together by ultrasonic welding in an overlapping region (9, 10).11. The accumulator according to claim 1, wherein said casing (2, 3) iscomprised entirely of plastic material (14, 24) and said casingcomprises two casing portions (2, 3) that have been joined together byretaining elements (30, 31) arranged in an overlapping region (9, 10).12. The accumulator according to claim 1, wherein said hard plasticmaterial (24) has glass fibers embedded therein.
 13. The accumulatoraccording to claim 1, wherein a desired-rupture location (15) isarranged as a portion of reduced thickness within a part of said casing(2, 3) that consists of said hard plastic material (24).
 14. Theaccumulator according to claim 1, wherein said casing (2, 3) has afilling opening (16) spaced closer to a positive pole contact (7) than anegative pole contact (8) and is closed with a plug (17) of T-shapedprofile.
 15. The accumulator according to claim 1, wherein said casing(2, 3) forms a part of a casing of an electrical device.
 16. Anaccumulator with a gas-tight and liquid-tight electrolyte filled casing,in which are arranged electrodes that are separated from each other by aseparator and are respectively electrically connected to pole contactsthat are accessible from outside of said casing, whereinin a region ofsaid pole contacts (7, 8) said casing (2, 3) comprises a soft plasticmaterial (14) and a hard plastic material that are fixedly connectedtogether, said soft plastic material (14) forms a seal for at least oneof said pole contacts (7, 8) and a feed-through ducting of said polecontacts, said casing (2, 3) is prismatic, said electrodes (5, 6) arearranged in super-imposed relationship in a layer-wise mannerrespectively separated by said separator (4), and connecting lugs (27,28) are arranged behind said pole contacts (7, 8), project laterallyfrom said electrodes (5, 6) and are electrically connected to each otherand to a respective pole contact.
 17. The accumulator according to claim16, wherein said casing (2, 3) is rectangular.
 18. The accumulatoraccording to claim 16, wherein said connecting lugs (27, 28) have beenconnected to each other and to respective pole contacts (7, 8) by spotwelding.